This invention concerns thermoforming apparatus and more particularly drive mechanisms for advancing plug assists into mold cavities as an aid in stretching the material into conformity with the mold cavity walls.
In this technique, an array of plugs are moved on a “third” platen very quickly into the mold cavities during the forming cycle, i.e., completing the movement within one quarter of a second is typical.
In order to accomplish this, in the past, a set of four ball screws was arranged well outside the center of the machine which collectively drove a large plate to which were affixed a series of pusher shafts which in turn were coupled to a tooling third platen on which an array of plugs were mounted.
The use of a plurality of ball screws necessitated an arrangement of drive belts or other means interconnecting the ball screws to synchronize their rotation to maintain the proper orientation of the tooling platen. An overly complex assembly resulted and notwithstanding the interconnection, the ball screws were difficult to keep in perfect synchronization. The platen was of necessity quite large to accommodate the four ball screws, and needed to be guided in linear bearings engaging the outer sides of the platen.
Also, the large size of this assembly precluded any protective enclosure of the components, allowing dirt to enter and lubricant to escape from these components.
It is the object of the present invention to provide a plug assist drive of the type described which is much simpler and more compact to allow an enclosure of the components.
It is a further object of the present invention to provide such a plug assist drive which has fewer components which are more compactly arranged and which is easy to disassemble.